A conventional data communication protocol assumes that, when one computer includes only one processor, this one processor serves as a representative to communicate with another computer, and when one computer includes multiple processors, one of the multiple processors serves as a representative to communicate with another computer.
When two computers carry out a secure communication therebetween, usually, a user of one computer and a user of the other computer exchange public key certificates (electronic certificates) to carry out the secure communication, or the computers use the secure socket layer (SSL) (or transport layer security (TLS)), a client computer obtains a public key accompanying a public key certificate from a server computer, and then, they secretly share a common key generated on one of them, thereby realizing a secure data communication between the client and the server.